Continuous mixing apparatus



y 1965 J. L. BROWNING ETAL 3,193,991

CONTINUOUS MIXING APPARATUS Filed Sept. 25, 1963 K m R A O P 2 GT M l Um m p m w w a "DO U m 5 C C H 2 W C O G a m T m 4 2 s T 2 2 A L C H I 6J 4 2 E9 8 LR M2 2 A L GT P A FR h RA L S l TP A 2 NE 8 G R ES GE C 4 mmMA MW .6 O rm 2 m 4 S 8 DD D WE m u E WHT 7 INVENTORS. JOE L. BROWNINGALBERT J. co

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United States Patent "ice 3,193,991 CONTINUUUS MlXlNG APPARATUS Joe L.Browning and Albert J. Colli, Indian Head, Md, assignors to the UnitedStates of America as represented by the Secretary of the Navy FiledSept. 25, 1963, Ser. No. 311,597 7 11 Claims. (Cl. 55185) (Granted underTitle 35, U.S. Code (1952), see. 266) The invention described herein maybe manufactured and used by or for the Government of the United Statesof America for governmental purposes without the payment of anyroyalties thereon or therefor.

This invention relates to mixing apparatus, and more particularly to anapparatus for continuously mixing liquids with pneumatically conveyedsolids.

In the past, the techniques utilized for continuously mixing the solidand liquid constituents of rocket propellants have possessed manyinherent dangers and problems due to the nature of the apparatus whichit was necessary to utilize. For example, continuous helical mixers havebeen used in which the solid and liquid constituents move slowly throughthe groove of a mixing screw and are blended by the resultant agitation.Mixers of this type are dangerous for the manufacture of propellantsbecause of the possibility of having particles caught and fracturedbetween moving parts with a resultant explosion. Also, helical mixershave a relatively large hold-up and small capacity for their size.

Continuous mixing of propellant constituents has also been accomplishedin the past in blending machines wherein the solids are carried by aninert liquid diluent. There are many problems associated with theremoving of the liquid diluent from the mix, however, and the uncertaineifect of small residual amounts of diluent in the product poses furtherproblems. Also, it is very diflicult to accurately meter the slurry inorder to obtain proper proportioning of the various constituents.Manifestly, it would be highly desirable if a continuous mixingapparatus could be provided, for mixing particulate solid and liquidconstituents, which was free of the aforedescribed disadvantages.

It is therefore a primary object of the present invention to provide anew and improved continuous mixing apparatus.

It is another object of this invention to provide a new and improvedmixing apparatus for continuously blending particulate solid materialswith liquid constituents.

It is a further object of the present invention to provide a continuousmixing apparatus wherein the mixing chamber has no moving parts.

It is yet another object of the present invention to provide acontinuous mixing apparatus having a relatively small hold-up inrelation to its size.

With these and other objects in view, the present invention contemplatesa continuous mixing apparatus including an elongated, porous-wall tubeinto which metered quantities of pneumatically conveyed solidparticulate materials are inserted. The liquid or liquids to be blendedwith the solid materials are injected into the gas stream adjacent theentrance end of the porous tube. An addi tional supply of the carriergas is introduced into a manifold surrounding the porous tube and flowsrapidly through the pores of the tube wall. The gas flowing through thetube wall will move the solid particles and liquid droplets in a randommanner as if fully developed turbulent flow were established in aconventional pipe. Also, the gas entering the tube through the wallsthereof will also serve to reduce the drag between the materials in theporous tube and the tube wall. A centrifugal separator receives theoutput of the porous tube and separates the carrier gas from the solidand liquid mixture.

3,1933% Patented July 13, 1955 The carrier gas exiting from acentrifugal separator is filtered and recompressed for further use,while the solid and liquid mixture is withdrawn from the bottom of theseparator through a slit plate and cast into the desired form.

Other objects, advantages and novel features of the invention willbecome readily apparent upon consideration of the following detaileddescription when read in conjunction with the accompanying drawingswherein:

FIG. 1 is a schematic representation of the system embodying the presentinvention;

FIG. 2 is an enlarged view, partially in section, of the mixing chamberof the present invention;

FIG. 3 is a sectional view taken along the line 33 of FIG. 2 furtherenlarged and illustrating the relative arrangernent of the porous mixingtube, surrounding manifoldand carrier gas supply pipes; and

FIG. 4 is a sectional view taken along the line 44 of FIG. 3 furtherenlarged and illustrating the arrangement of nozzles on the inner wallof the delivery tube which serve to inject the liquid constituent intothe gas stream within the delivery tube.

Attention now is directed to the drawings, wherein like numerals ofreference designate like parts throughout the several views, and moreparticularly to FIG. 1 for a description of the operation of thecontinuous mixing apparatus of the present invention. The systemcomprises a carrier gas tank 10 connected to a supply line 11 through aregulating device 12. The particular conveying gas used will be dictatedby the nature of the solid and liquid ingredients to be mixed.Naturally, the gas will be one which will not react with any of thepropellant constituents. The regulating device 12 is not shown in detailand may be any suitable type which will permit regulation of the rate ofdischarge of gas from the tank 10 and hence the velocity of theconveying gas through the system which in turn controls the mixing rate.A plurality of solid feeders 14 are connected to the supply line 11 andare provided for metering predetermined quantities of the solidparticulate constituents of the propellant into the gas stream withinthe supply line 11. The specific nature of the feeders 14 will of coursebe dictated by the properties of the solid materials to be handled.

The supply line 11 is connected by means of a delivery tube 15 to amixing chamber, designated generally by the reference numeral 16. Aliquid feeder 18 is connected to the delivery tube 15 by means of aliquid feed line 19. The liquid feeder 18 may be of any suitable typewhich is capable of providing an adjustable flow rate. Aninterconnection between the supply line 11 and the mixing chamber 16 isprovided by a bypass line 26 and connecting branch lines 21.

A centrifugal separator 22 is connected to the exit end of the mixingchamber 16. The separator 22 is coupled to a filter 24 and a compressor25 through a discharge line 26. The compressor 25 serves to Withdraw theconveying gas from the separator 22 through the filter 24, and then toreturn the recompressed gas to the gas tank It The bottom of theseparator 22 is connected to a casting chamber 28 through a slit plate29. The solid and liquid mixture is withdrawn through the slit plate 29into the casting chamber 28 and is then cast into the desired shape. Avacuum pump 30 is provided for degassing the solidliquid mixture bymaintaining a vacuum over the material being drawn through the slits.The output of the vacuum pump 30 is returned to the system through thedischarge line 26 at a point adjacent the intake of the compressor 25. V

V The mixing chamber'16 will now be described in further detail withparticular reference to FIGS. 2, 3 and 4. The mixing chamber comprises acylindrical porous walled tube 31 which is disposed within and coaxialwith a cylindrical manifold 32. The manifold 32 has a plurality ofapertures formed therein which accommodate the ends of the branch lines21. A hollow-walled section 34 is formed on the end of the delivery tubeand projects a short distance into the entrance end of the porous mixingtube 31. A plurality of nozzles 35 are formed by holes drilled throughthe inner wall of the hollowwalled section 34, and as can be best seenin FIG. 4, the nozzles 35 are uniformly spaced about the periphery ofthe inner wall of the section 34. It will be noted that the nozzles 35are in fluid communication with the interior 36 of the section 34 whichis in turn in fluid communication with the liquid supply line 19.

Operation In order that a better understanding of the invention might behad, its mode of operation will now be described. Gas fiow is initiatedin the supply line 11 and brought up to the desired velocity by means ofthe regulator 12. The vacuum pump 30 is then started. The solid feeders14 are next started and begin metering quantities of solid particulatematerial at a predetermined rate into the gas stream in the line 11 tobecome entrained therein. The liquid feeder 18 is then started and setto deliver at the desired rate. The liquid constituent will flow throughthe feed line 19, into the interior space 36, and then out through thenozzles 35 to impinge upon the stream of gas and entrained solids atright angles thereto. This begins the mixing operation.

Additional conveying gas will fiow through the bypass line 20 and intothe interior of the manifold 32 through the branch lines 21. Thebypassed gas will then flow through the pores of the mixing tube 31 andinto the interior thereof. The additional gas flowing through the poresof the mixing tube 31 will establish a velocity gradient along themixing tube 31 with the exit velocity of the gas stream beingsignificantly higher than the entrance velocity. The solid-liquidmixture entrained in the gas stream will, of course, be acceleratedalong with the gas although at a lesser rate. The lesser acceleration ofthe solid-liquid mixture and the introduction of additional gas throughthe pores of mixing tube 31 will result in a continuous reduction in theconcentration of material in the gas stream. Under these circumstances,the conditions of turbulent fiow in a conventional pipe have beenduplicated and thorough mixing is achieved.

By disposing the nozzles 35 perpendicular to the high velocity gasstream in which the solid particles are entrained, the kinetic energy ofthe liquid stream is used to penetrate the gas stream so that the liquidis suddenly subjected to a high velocity gas. The liquid is introducednear enough to the mouth of the delivery tube 15 so that the droplets ofliquid do not impinge upon the tube Wall. This is accomplished by sizingthe cross-sectional area of the nozzles 35 so that the resultantvelocity vector will allow the liquid to converge outside of the tube. Asheet of extremely small liquid droplets evenly distributed over thecross-section is formed outside the mouth of the tube 15. By making thisliquid sheet sufiiciently dense, a very high percentage of thepneumatically conveyed solids will be immediately exposed to the liquid.The turbulent fiow conditions and acceleration effects in the remainderof the mixing tube 31 will then serve to complete the mixing process andproduce a solid-liquid mixture which is substantially homogeneous.

Upon leaving the mixing chamber 16, the conveying gas stream and theentrained solid-liquid mixture enter the centrifugal separator 22 forseparation of the gas from the solid-liquid mixture. The gas leaving thetop of the separator will be filtered, recompressed and then returned tothe gas tank 10 for recycling. The solidliquid mixture is continuouslywithdrawn from the bottom of the separator through a slit plate and castinto the desired shape. The vacuum pump 30 will, as previouslymentioned, serve to degasthe mixture by maintaining a vacuum over thematerial being drawn through the slits.

From the foregoing, it, Will be readily apparent that the presentinvention provides a new and improved continuous mixing apparatuspossessing numerous advan tages not attainable with prior art devices.For example, the consistency of the material to be mixed will not be asensitive parameter to the degree of dispersion. What would be a thick,relatively immobile mass in a conventional mixer, in the presentinvention will be a particulate mixture entrained in a carrier gas.Also, since the present invention involves no moving parts within themixing chamber, a hazard of considerable significance in the mixing ofpropellants and explosives is eliminated. And further, the entire systemincluding the feeders, mixer, centrifugal separator, casting chamber andcompressor could be closed for the mixing toxic materials.

Certain modifications of the disclosed embodiment will immediatelysuggest themselves to those skilled in the art. For example, a series ofgrooves could be cut out of the exterior surface of the mixing tube 31.The velocity of the carrier gas through the grooved channel would thenbe greater than through the thicker porous section. The stream of highervelocity gas through the channel would form a continuous helicoidextending the length of the tube. An approach of this kind might enablea still higher degree of dispersion to be attained. Also, although theillustrated embodiment shows only a single liquid feeder, it is manifestthat additional liquid feeders could be provided with mixing of theliquid constituents taking place in the interior space 36 or in themixing tube 31 through the provision of separate sets of nozzles foreach liquid.

It is to be understood that the disclosed embodiment simply represents apreferred form of the present invention. Numerous other arrangements maybe readily devised by those skilled in the art to achieve a similarapparatus still embodying the principles of the present invention andfalling within the spirit and scope thereof.

What is claimed is:

1. An apparatus for continuously mixing liquids withpneumatically-conveyed, particulate solids comprising a porous tube,

means for injecting in one end of said tube a stream of gas havingparticulate solids entrained therein, means disposed in said one end ofsaid tube for introducing liquid into said gas stream,

and means including a manifold surrounding said tube for applyingpressurized gas to the exterior of said tube whereby turbulent flowwithin said tube is produced by gas flowing into said tube through thepores thereof.

2. The mixing apparatus of claim 1 wherein the liquid is introduced in adirection substantially perpendicular to the flow direction of said gasstream.

3. The mixing apparatus of claim 1 wherein the other end of said tubeempties into a centrifugal separator,

said separator serving to separate the conveying gas from thesolid-liquid mixture.

4. The mixing apparatus of claim 3 wherein means are provided forcompressing the gas output from said centrifugal separator andrecirculating said gas to entrain further particulate solid matter.

5. An apparatus for continuously mixing liquids withpneumatically-conveyed, particulate solids comprising a porous mixingtube,

a delivery tube coaxial with said mixing tube and projecting into oneend thereof,

means for supplying to said delivery tube a high velocity stream of gashaving particulate solids entrained therein,

means disposed on the inner end of said delivery tube for injectingliquid into said gas stream in a direction substantially perpendicularthereto,

and means including a manifold surrounding said bulent flow within saidmixing tube is produced by gas flowing into said tube through the poresthereof.

6. The mixing apparatus of claim 5 wherein said delivery tube is ahollow walled tube,

and said liquid injecting means includes a plurality of nozzles formedon the inner wall of said delivery tube adjacent the end thereof.

7. The mixing apparatus of claim 5 wherein a centifugal separator iscoupled to the other end of said porous mixing tube for separating theconveying gas from the solid-liquid mixture.

8. The mixing apparatus of claim 7 wherein means are provided forcompressing the gas output from said centrifugal separator andrecirculating said gas to entrain further particulates sol-id matter.

9. An apparatus for continuously mixing liquids with pneumaticallyconveyed particulate solids comprising a delivery tube,

means for creating a ligh velocity gas stream within said delivery tube,

means for metering solid particulate materials into said delivery tubeupstream of the exit end thereof,

a porous-walled mixing tube coaxial with said delivery tube,

a hollow-walled section formed on the exit end of said delivery tube andprojecting into the entrance end of said mixing tube,

a plurality of nozzles formed on the inner wall of said hollow-Walledsection,

means for feeding liquid into said hollow walled section for injectioninto said gas stream through said nozzles,

and means including a manifold surrounding said porous mixing tube forapplying high pressure gas to the exterior of said mixing tube wherebyturbulent flow within said mixing tube is produced by gas flowing intosaid mixing tube through the pores thereof.

10. The mixing apparatus of claim 9 wherein a centrifugal separator iscoupled to the exit end of said mixing tube for separating the conveyinggas from said solidliquid mixture.

11. The mixing apparatus of claim 10 wherein means are provided forfiltering and recompressing the gas output from said separator and forreturning said gas to said gas stream creating means.

References Cited by the Examiner UNITED STATES PATENTS 1,934,840 11/33Claude].

2,294,973 9/42 Ford 261122 2,884,375 4/59 Seelig et al. 2594 XR2,951,061 8/60 Gomory 2594 XR 3,153,578 10/64 Taylor 2594 XR WILLIAM J.STEPHENSON, Primary Examiner.

1. AN APPARATUS FOR CONTINUOUSLY MIXING LIQUIDS WITHPNEUMATICALLY-CONVEYED, PARTICULATE SOLIDS COMPRISING A POROUS TUBE,MEANS FOR INJECTING IN ONE END OF SAID TUBE A STREAM OF GAS HAVINGPARTICULATE SOLIDS ENTRAINED THEREIN, MEANS DISPOSED IN SAID ONE END OFSAID TUBE FOR INTRODUCING LIQUID INTO SAID GAS STREAM, AND MEANSINCLUDING A MANIFOLD SURROUNDING SAID TUBE FOR APPLYING PRESSURIZED GASTO THE EXTERIOR OF SAID TUBE WHEREBY TURBULENT FLOW TITHIN SAID TUBE ISPRODUCED BY GAS FLOWING INTO SAID TUBE THROUGH THE PORES THEREOF.